ANAEROBIC AND AEROBIC DEGRADATION OF PYRIDINE BY A NEWLY ISOLATED DENITRIFYING BACTERIUM

New denitrifying bacteria that could degrade pyridine under both aerob ic and anaerobic conditions were isolated from industrial wastewater. The successful enrichment and isolation of these strains required sele nite as a trace element. These isolates appeared to be closely related to Azoarcus species according to the results of 16S rRNA sequence ana lysis, An isolated strain, pF6, metabolized pyridine through the same pathway under both aerobic and anaerobic conditions, Since pyridine in duced NAD-linked glutarate-dialdehyde dehydrogenase and isocitratase a ctivities, it is likely that the mechanism of pyridine degradation in strain pF6 involves N-C-2 ring cleavage. Strain pF6 could degrade pyri dine in the presence of nitrate, nitrite, and nitrous oxide as electro n accepters. In a batch culture with 6 mM nitrate, degradation of pyri dine and denitrification were not sensitively affected by the redox po tential, which gradually decreased from 150 to -200 mV, In a hatch cul ture with the nitrate concentration higher than 6 mM, nitrite transien tly accumulated during denitrification significantly inhibited cell gr owth and pyridine degradation, Growth yield on pyridine decreased slig htly under denitrifying conditions from that under aerobic conditions, Furthermore, when the pyridine concentration used was above 12 mM, th e specific growth rate under denitrifying conditions was higher than t hat under aerobic conditions, Considering these characteristics, a new ly isolated denitrifying bacterium, strain pF6, has advantages over st rictly aerobic bacteria in field applications.